Environment and Natural Resources
Environment and Natural Resources covers ecosystems, food chains, energy flow, biogeochemical cycles, pollution and conservation of water, soil and forests.
Core ideas
- An ecosystem includes biotic communities and abiotic factors interacting. Producers make food; consumers eat; decomposers break down dead matter.
- A food chain shows feeding relationships; arrows point in the direction of energy flow. Food webs are more realistic because organisms eat several things.
- Energy flow is one-way. About 10% of energy passes to the next trophic level; most is lost as heat and used in life processes.
- Biogeochemical cycles include the water, carbon, nitrogen and oxygen cycles. Decomposers return nutrients to the soil.
- Pollution includes air, water, soil and noise pollution. Greenhouse gases trap heat; ozone in the stratosphere shields Earth from ultraviolet radiation.
- Natural resources need sustainable use: rainwater harvesting, afforestation, soil conservation and recycling.
Worked example
If producers contain 10,000 J of energy, how much reaches a tertiary consumer? Apply the 10% law at each step: primary consumer 1,000 J; secondary consumer 100 J; tertiary consumer 10 J. Reasoning: only about one-tenth is transferred at each level, so long food chains support fewer top consumers.
Traps that cost marks
Arrows in a food chain show energy flow, not who eats whom in reverse. Ozone depletion and global warming are different problems: ozone shields from UV; greenhouse gases trap heat. Decomposers are not consumers in the usual grazing sense. Do not say energy is recycled; matter cycles, energy flows.